(a) Field of the Invention
The present invention relates to a regenerative braking system for a fuel cell vehicle and, more particularly, such a braking system using a super capacitor.
(b) Description of the Related Art
Generally, a fuel cell includes electrodes where electrochemical reaction occurs, an electrolyte membrane transmitting hydrogen ions generated by the reaction, and a separator supporting the electrodes and the electrolyte membrane. A polymer electrolyte fuel cell is widely used as a fuel cell for a vehicle. The polymer electrolyte fuel cell is a device generating electricity while generating water and heat through electrochemical reaction between hydrogen and oxygen.
The polymer electrolyte fuel cell has a better efficiency, greater current density and output density, and shorter starting time than fuel cells of other types. It is also free from corrosion and does not need to regulate the electrolyte. Furthermore, the polymer electrolyte fuel cell is a green power source that exhausts pure water, so various research regarding the same is being made in the field of an automotive engineering.
Recently, a super capacitor has been explained for fuel cell vehicles in addition to a battery. The super capacitor is charged while a vehicle runs, and the super capacitor serves to supplement power of a fuel cell stack.
The super capacitor assists power during acceleration of a vehicle and stores regenerative braking energy while applying brake. The super capacitor should be suitably charged and discharged so as to supplement operation of a fuel cell vehicle, and overcharge of the super capacitor may cause problem in an overall system of a fuel cell vehicle. In particular, in case that a fuel cell vehicle having the super capacitor is repeatedly braked while driving a downhill, there is a problem in that the brake may be overloaded and the super capacitor may be overcharged.